The present invention generally relates to structures and methods for shielding electromagnetic waves using graphene, and more particularly, to methods and structures of doped graphene sheets configured to reflect and/or absorb the electromagnetic waves being emitted from a electromagnetic wave generating source.
Emission of electromagnetic (EM) radiation at radio, microwave and terahertz frequencies is known to interfere with operation of electronic devices and has been linked to various health hazards to exposed individuals. For example, the World Health Organization has recently announced that exposure to microwave radiation could increase the risk of brain cancer. Because of concerns such as these, EM radiation is a serious issue and attempts to provide various shielding materials and devices have evolved. Most commonly used EM shields in use today are fabricated from metallic films, metallic grids, metallic foams, or powders on glass or plastic substrates. One example is a shielded cable, which has electromagnetic shielding in the form of a wire mesh surrounding an inner core conductor. The shielding impedes the escape of any signal from the core conductor, and also signals from being added to the core conductor. Some cables have two separate coaxial screens, one connected at both ends, the other at one end only, to maximize shielding of both electromagnetic and electrostatic fields. Another example is the door of a microwave oven, which typically has a metallic screen built into the window. From the perspective of microwaves (with wavelengths of 12 cm) this screen in combination with the oven's metal housing provides a Faraday cage. Visible light, with wavelengths ranging between 400 nm and 700 nm, passes easily between the openings the metallic screen whereas microwaves are contained within the oven itself.
Due to the inherent weight of metallic shields, the added weight can be significant. Moreover, many of the currently available EM shields are not transparent, which can be a significant disadvantage for many applications. Conventional transparent and conductive materials such as indium tin oxide (ITO) and zinc oxide (ZnO) have been applied to transparent substrates such as glass and plastics for EM shielding. However, the use of these types of transparent EM shields is fairly limited in their use because the shielding effectiveness of these materials is generally low, the shield itself is typically inflexible, and these types of EM shields provide limited mechanical strength. Providing higher EM effectiveness with these types of materials requires increased thicknesses, which then affect transparency.